In recent years, the pace of large-scale popularization of new energy vehicles has become increasingly faster. As a core component of the new energy vehicles, the power battery system has a direct impact on the performance of the vehicle. The power battery system is composed of a plurality of power battery cells connected in series. Due to the limitation of the process conditions and differences in the characteristics of the battery itself, there may be differences in electric quantity or voltage between the battery cells. After multiple cycles of charging and discharging, the differences in the electric quantity and the voltage of the cells becomes larger and larger. As a result, a charging/discharging capacity of the power battery system becomes smaller and smaller, thereby directly affecting the operational performance and the lifetime of the power battery. Therefore, the electric quantity and the voltage of the power battery in an equalizing state may improve the charging/discharging performance and the service lifetime of the power battery. At present, common-used battery equalization methods include active equalization and passive equalization. The active equalization is also known as lossless equalization, which transfers electric quantity from a battery cell with high electric quantity to a battery cell with low electric quantity, or supplements the battery cell with low electric quantity by external energy. The active equalization has an advantage of high equalization efficiency, but the active equalization system is relative complicated and has a high cost, and there is less practical application at present. The passive equalization, also known as lossy equalization, makes the surplus electric quantity in the battery cell with high electric quantity to be discharged by connecting resistors in parallel. The equalization efficiency of the passive equalization is lower than that of the active equalization. However, the passive equalization has a simple circuit structure, a low cost and a wide range of practical applications.
A power battery passive equalization system in prior art generally monitors an open-circuit voltage of the power battery cell in a standing state in real time after the charging of the power battery is finished, and determines a to-be-equalized battery cell in real time and achieves the equalization of the battery system. A target of the equalization is a difference between the open-circuit voltages of the battery cells satisfying a required value, while the passive equalization function generally does not work during the charging/discharging process of the battery. Since the equalization is performed only during a standing process of the power battery, the equalization time is too short, leading to a low equalization efficiency.
In view of the above problems, no effective solution has been proposed.